The first law of photochemistry states that light has got to be absorbed before photochemistry can occur, which stresses the importance of cellular absorption (Smith, 1981). Typically, photobiological effects are both wavelength and dose-dependent, and result from chemical and/or physical changes induced by non-ionizing radiation (Anderson and Parrish, 1981). When used at a proper wavelength, light activation of enzymes and other tissue components leads to changes in metabolism and induces metabolic modulations.
As light energy is absorbed within the skin, light can be used to achieve desired clinical results. In particular, light has been used to remove vessels, hair, eliminate leg veins, remove or reduce the color of tattoos. In addition, water absorption of light energy transforming light into heat energy has been used for laser ablation of the skin surface or for use of lasers as cutting instruments. Plastic surgeons, dermatologists and their patients continually search for new and improved methods to alter the appearance of the skin.
Since 1970, Low Level Laser Therapy (LLLT), non-thermal, non ablative energy, has been used in phototherapy to speed up wound recovery, to promote angiogenesis and in physiotherapy, to treat musculoskeletal injuries (Basford, 1986; Wheeland, 1993; Conlan et al., 1996; Schindl and Schindl, 2000; Whelan et al., 2001). Light-induced physiological responses can also promote collagen production and accumulation to promote skin appearance and enhancement of skin texture (Yamamoto et al., 1996; Barolet et al., 2005).
The adjustment of various parameters was found to enhance dermal collagen production using non-ablative, non-thermal light source. For instance, specific wavelengths were able to induce increased growth characteristics in fibroblasts (Bosatra et al., 1986; Yamamoto et al., 1996; Almeida-Lopes et al., 2001; Vinck et al., 2003). The fluence, or total dose of energy distributed over a given amount of time, as well as irradiance or the total light intensity reaching the cell are also thought to be involved. In fact, it is suggested that the cellular threshold irradiance would have to be reached to induce a proper physiological stimulation for collagen synthesis within a relatively narrow window of opportunity (Sommer et al., 2001).
Fluence and irradiance are independent variables to be considered in order to generate a specific physiological effect, as even prolonged but insufficient irradiance exposure could have no physiological benefit if the irradiance threshold is not surpassed (Sommer et al., 2001). Finally, pulse duration in microsecond domains that demonstrated an increase in dermal collagen with the pulsed dye laser at 585 nm in earlier studies (Bjerring et al., 2002; Moody et al., 2003) is applied to LED science and pulsing patterns are being elaborated to increase cellular stimulation (Weiss et al., 2005; Barolet et al., 2005).
Photochemistry/biology happens when a chromophore absorbs light energy. The chromophore can be a true color pigment such as black, brown, or red pigments, or a molecule absorbing energy, such as water or a protein complex. Selective chromophore absorption is the absorption of a particular type of light energy by a chromophore. A clinical light treatment typically works because of selective chromophore absorption, wherein light energy is selectively absorbed by a particular component of the skin.
It has been proposed that light-activated enzymes of respiratory chains like mitochondrial NADH-dehydrogenase, and cytochrome c oxidase could act as photoacceptors promoting mitochondrial redox activity and cellular redox state (Karu, 1999; 2004). Therefore, the dermal fibroblast mitochondrial cytochrome c oxidase is thought to act as an endogenous chromophore. Light activation of cellular component at a proper wavelength was found to induce metabolic modulations correlating with tissue response (Smith, 1981; Anderson et al., 1981; Bihari and Mester, 1989; Yu et al., 1994; Almeida-Lopes et al., 2001 Wheeland et al., 2001). Wavelengths around 660 nm were found to reach through the whole papillary layer to enhance collagen production (Webb et al., 1998,). Such non-thermal non-ablative light treatment mainly targets the dermal fibroblast to enhance collagen production and improve skin texture. However it has little or no effects on the epidermis.
PhotoDynamic Therapy (PDT) is another way to use light to enhance skin appearance. However, PDT typically involves the application of a topical photosensitizer that once activated by irradiation induces tissue necrosis. Necrosis results from selective accumulation of the activated photosensitizer in diseased tissue, which generates free radicals. First used as a treatment modality for various cancers, PDT is nowadays undergoing rapid development for cosmetic applications. Indeed, PDT is emerging as a powerful new tool to boost clinical results of non-ablative laser and/or light therapy in the treatment of aged and sun damaged skin, as well as acne. The application of a light-sensitizing solution to skin marred by scaly lesions, skin blotchiness and enlarged pores, followed by the delivery of a light treatment appears to enhance cosmetic skin appearance by improving skin tone, skin texture and pore size. However downtime must still be anticipated, such as redness, crust or more severe side effects that demands longer recovery time.
The epidermis is also targeted to enhance skin general appearance. It has been found that retinol, retinol derivatives, pentapeptides and copper peptides have enhanced efficacy to affect cellular proliferation and differentiation, having a surprising effect in reducing signs of photodamage or aging skin (appearance of fine lines) hyperpigmentation and age spots. Topical creams promote flexibility of the stratum corneum, increasing the content of collagen, and/or glycosaminoglycans in skin, increasing skin moisture, and decreasing transcutaneous water loss to obtain enhanced global skin appearance.
However, some powerful topical agents can irritate the skin. For example, tretinoin used in potent anti-wrinkling regimens and proven to stimulate collagen production in the dermis but may cause erythema, reducing compliance to the treatment. Moreover, light-based techniques used to enhance skin appearance typically target dermal fibroblasts but have little effect on the epidermis.
In view of the above, there is a need in the industry to provide a novel method for the treatment of mammalian skin tissues.
An object of the present invention is therefore to provide a novel method for the treatment of mammalian skin tissues.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.